Tubular fluid heater and support therefor



Jan. 31, 1967 J. E. INGERSOLL TUBULAR FLUID HEATER AND SUPPORT THEREFOR Filed 001;. 8, 1965 2' Sheets-Sheet l FIG.6

INVENTOR.

James E. lngersoll ATTORNEY Jan. 31, 1967 J. E. INGERSOLL 3,301,227

TUBULAR FLUID HEATER AND SUPPORT THEREFOR Filed "0t. 8, 1965 2 Sheets-Sheet 2 F|G.2 j

I J H ll ll 3;? HQ) 45F nited States 3,361,227 Patented Jan. 31, 1967 TQQ 3,301,227 TUBULAR FLUID HEATER AND SUPPORT THEREFOR James E. Ingersoll, Clinton, ()hio, assignor to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Filed Oct. 8, 1965, Ser. No. 494,073 Claims. (Cl. 122510) This invention relates generally to tubular fiuid heaters and their support, and more particularly to the support of a tubular fluid heater within an upfiow high temperature heating gas pass of a vapor generator.

Heretofore, superheater tube banks and the like formed of horizontal nested return-bend tubes in platen elements adapted to span an upright gas pass were gene-rally end supported on opposed upright fluid-cooled tubes by means of complimentary support attachments externally welded to the return bend portions of the platen elements and to the adjacent wall support tubes respectively. For example, a typical support arrangement that has been successfully used in many installations as shown in US. Patent 3,055,349, issued September 25, 1962, in the name of Hamilton et al.

In installations where relatively high heating gas temperatures are required to provide the desired steam temperature control range, and particularly in such units fired with oil containing substantial amounts of sulphur and/or vanadium, the support attachments have been found to be subject to accelerated high temperature corrosion from the oxide forms of these chemicals when the metal temperature of the attachments exceeds approximately 1100 F. This condition is particularly prevalent in those installations where the high temperature vapor heating tube bank, e.g. the secondary superheater, is arranged immediately adjacent the furnace chamber outlet so that it is exposed to furnace radiant heat in addition to high temperature gaseous combustion products.

The problem of adequately supporting secondary superheater tube banks in high temperature gas streams may be further aggravated when dissimilar metals are used in the tube bank platens. In this regard, it is common practice to use a high quality alloy in the first few (upstream) rows of a secondary superheater, with the remaining (downstream) rows being formed of lower alloy steel, since the tempuerature conditions in the downstream portion of the tube bank are much less severe and the use of higher alloys is not mandatory. In such instances, the problems attendant on the welding of support attachments (which are themselves formed of high alloy material) to the various alloy metals used in the tube bank requires judicious selection of the proper weld materials and welding techniques. Usually, all of the tube support attachments in the high temperature zone are of the alloy required to withstand the highest probable sustained metal temperature. This is done to minimize te possibility of catastrophic structural failure of the supports. As a further safeguard, the supports are preferably shielded from the main gas stream flow and are proportioned so that they contain the minimum volume of metal consistent with providing the requisite support for the imposed loadings.

It is therefore an object of the present invention to provide, for a tube bank disposed in a high temperature heating gas pass, a support arrangement whereby the alloy attachments are substantially shielded from the high temperature gas to reduce the temperature of the attachments and thereby avoid high temperature corrosion. It is a further object of this invention to provide for the support of the tube bank in a manner such that the main supporting attachment lugs connect only to the lower temperature downstream (gas flow-wise) end of the tube bank to thereby minimize the temperature of these lugs so as to avoid corrosion.

These and other objects are attained according to the present invention in a vapor generator having a furnace chamber wherein fuel is consumed to produce high temperature heating gas for upward passage through a heating gas pass bounded by a pair of opposed upright fluidcooled tubular walls. A tubular fluid heater, e.g. a secondary superheater, is arranged within the gas pass immediately adjacent the furnace outlet. The secondary superheater tube bank is formed of a plurality of spaced parallel tube platens which extend between and are supported by the opposed tubular walls. Each vertically disposed platen includes a pair of coplanar multi-looped tubes having horizontally extending straight portions and connecting tube bends, the tubes being alternately formed with inner and outer tube bends at opposite ends of the platen adjacent the Walls. Each platen is attached at its one end to the adjacent fluid cooled wall by a connecting lug which is welded to the uppermost outer tube bend of the platen to thereby support the tube portions connected with the uppermost outer tube bend. The remaining tube portions of the platen are supported from one of the straight tube portions connected with the directly supported uppermost outer tube bend by means of an inverted U-shaped tube which extends downwardly on both sides of the platen. A series of support bars extend between the legs of the inverted U-shaped tube and engage the lower tube loops of the platen. The U-shaped support tube is serially connected for flow of fluid therethrough with one of the lower tubes of the platen that it supports.

For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings in which:

FIG. 1 is a partially schematic sectional side elevation of a vapor generator employing a fluid heater (secondary super-heater) tube bank supported and arranged accord-.

ing to the present invention;

FIG. 2 is an enlarged side elevation of a platen of the secondary superheater shown in FIG. 1;

FIG. 3 is a sectional view taken along line 33 of FIG. 2;

FIG. 4 is a sectional view taken along line 44 of FIG. 2;

FIG. 5 is an enlarged sectional view taken along line 5-5 of FIG. 2; and

FIG. 6 is an enlarged view showing the details of support elements shown in FIGS. 2, 3 and 4.

Referring to FIG. 1, there is shown a natural circulation vapor generating unit having a furnace chamber 10 bounded by a front wall '11, rear wall 12, side walls 13, a pair of sloping floor sections 14 and a forwardly sloping furnace roof 15 overlying approximately the front half of the furnace chamber 10. Extending upwardly from the upper end of the roof 15 is a division wall 16 which divides the 'upper portion of the unit into an upflow heating gas pass 17 bounded on its outside by the upper end of the rear wall 12, and a downflow heating gas pass 18 bounded on its outer side by an upper front wall 11A. A roof 19 encloses the upper ends of the gas passes 17 and 18.

In operation, combustion air is supplied by a forced draft fan 21 via duct 22 to an air heater 35 for preheating. The heated air then passes to a Windbox 23 from whence is flows through the burners 24 wherein fuel is mixed with the air for combustion in the furnace chamber 10 to produce high temperature heating gas. The gas .passes from the furnace chamber 10 upwardly through the gas pass 17 and then downwardly through the gas pass 1 8 to the outlet 25, from which it passes in indirect heat exchange relation with the incoming air in the air heater 35 prior to being exhausted to the atmosphere. In passing through the gas passes 17 and 18, the heating gas passes serially over the secondary superheater 30, reheat superheat (two tube banks) 31, high temperature primary superheater 32A, low temperature primary superheater 32B and economizer (two sections) 33.

It should be understood that the above-described boundary walls are formed of contiguous tubular members through which feedwater is circulated from a steam and water drum 20 in a manner well known in the art. The steam generated in the tubes of the boundary walls passes from the steam drum 20 serially through the tube banks of the low temperature and high temperature primary superheaters 32B and 32A and the secondary superheater 30 to a high pressure turbine (not shown) for partial expansion. The steam is then returned to the unit and passes through the reheat superheater "31 from whence it is piped to a reheat turbine (not shown) for final expansion.

From the above, it can be seen that the .tubes of the secondary superheater 30 have the highest metal temperatures of any pressure parts in the unit because the secondary superheater 30 is positioned in the high gas temperature zone immediately adjacent the furnace outlet and has flowing therethrough steam at the final high outlet temperature.

Referring to FIGS. 2 through 5, the secondary superheater is arranged in two banks 30A and 308, the lower bank 30A being of particular importance in regard to the present invention since the tube support attachments of the lower bank 30A are subject to the higher gas temperatures.

Steam for passage through the secondary superheater 30 is supplied to the inlet header 40 which is located outside the rear wall 12 and extends horizontally parallel thereto. Each platen of the secondary superheater 30 is for-med with a pair of parallel flow coplanar multi-looped tubes 41 and 43 through which the steam passes to outlet header 44 which is arranged parallel to and above the inlet header 40. Each pair of tubes 41 and 43 is constructed with horizontally extending straight portions and connecting tube bends, the pair of tubes generally being alternately formed with inner and outer tube bends at opposite ends of the platen adjacent the upper tubes 12A of the rear wall 12 and the tubes 16A of the division wall 16.

Each platen of the lower section 38A is connected for support purposes at its inner and outer ends respectively to the division wall 16 and the upper rear wall tubes 12. At the inner end (adjacent the division wall 16) of the platen, a pair of support lugs 50 are welded on opposite sides of the uppermost outer tube bend 43A. The lugs 50 rest within recesses 51A formed in support blocks 51 that are welded to the mutually adjacent sides of a pair of spaced division wall tubes 16A (see FIG. It should be noted that the division wall tube 16B that would normally be between and in the same plane as the two supporting tubes 16A has been off-set so as to form a recess 55 in the division wall 16 wherein the lugs 50 and blocks 51 are disposed. The wall tube 16B is interconnected along its length to the adjacent tubes 16A by vertically extending web members 52 to avoid the bypassing of heating gas through the division wall 16. By thus arranging the lugs 50 and blocks 51 within the recess 55 where they are out of the main heating .gas stream and are cooled by the Wall tubes 16A and 16B and the tube bend 43A, the

temperature of these parts is minimized so that the possibility of high temperature corrosion is substantially eliminated. The other end of the platen (adjacent the rear wall 12) is supported by the rear wall 12 by means of a similar lug and block assembly that connects with the uppermost outer tube bend 41A.

The lower tube loops of the inner end of the platen are supported by an inverted U-shaped tube portion 41B of the tube 41 (see FIGS. 2 and 3). The U-bend of the tube portion 41B is engaged with the uppermost straight portion of tube 43, and the legs of the tube portion 41B extend downwardly along the platen on opposite sides thereof. Each of the intermediate outer tube loops (two shown) rest on support bars 56 which are welded between the legs of the tube portion 41B. Spacer blocks 57 are provided between adjacent tubes where necessary, the blocks 57 being of the type provided for and described in the aforementioned US. Patent 3,055,349, so that horizontal relative expansion and contraction movements can be accommodated between adjacent inner and outer tube loops. FIG. 6 shows a typical support bar 56 and block 57 and their relationship to the tube portion 4113. The lower tube loops of the other (outer) end of the platen are supported in a similar manner (see FIGS. 2 and 4) by the inverted U-shaped tube portion 438 of the tube 43.

From the above it can be seen that the individual tube loops of each platen of the lower superheater section 30A are adequately supported. It should be particularly noted that no support attachments are required at the lower end of the section; moreover, the pair of leg and block attachment assemblies for each platen are at the uppermost end of the platen where gas temperatures are lowest. It should also be noted that the heat absorption of the tubes 41 and 43 will be substantially equal since equal lengths of each are used to form the inverted U-tube supports.

What is claimed is:

1. A fluid heater comprising walls defining a heating chamber, means for passing high temperature heating gas through said heating chamber, and a tubular heat exchange platen within said chamber and having one end thereof adjacent one of said walls and including a multiplicity of coplanar multi-looped tubes having pairs of parallel straight portions connected at their ends by tube bends adjacent said one wall, lug means attaching the uppermost tube bend of said platen to said one wall to thereby support the straight port-ions connected with said uppermost tube bend, and means for supporting the remaining straight portions from one of the straight portions connected with said uppermost tube 'bend, said last named means comprising an inverted fluid-cooled U-shaped tube connected in load-bearing relationship with one of the straight portions connected to said uppermost tube bend, the legs of said U-shaped tube extending downwardly on opposite sides of said platen, and support bars extending between the legs of said U-shaped tube.

2. In a vapor generator, walls defining a furnace chamber, means for supplying fuel to said furnace chamber for combustion therein to produce high temperature heating gases, means defining a furnace outlet at the upper end of said furnace chamber, a pair of opposed upright fluidcooled walls defining a heating igas pass communicating at its inlet end with said furnace outlet, and a tubular fluid heater arranged within said gas pass immediately adjacent said furnace outlet, said fluid heater including a plurality of tube platens extending between and supported by said pair of walls, each of said platens including a pair of coplanar rnulti-looped tubes having horizontally extending straight portions and connecting tube bends, said walls alternately being formed with inner and outer tube bends at opposite ends of said platen adjacent said walls, lug means attaching the uppermost outer tube bend at each end of said platen to said walls to thereby support the straight portions connected with said uppermost outer tube bends, and means for supporting the remaining straight portions, said last named means comprising an inverted U-shaped tube engaged with one of the straight portions connected with one of said uppermost outer tube bends and extending downwardly therefrom on both sides of said platen, support bars extending between the legs of said U-shaped tube, said U-shaped tube being serially connected for flow of fluid therethrough with one of the tubes of said platen.

3. In a vapor generator, walls defining a furnace chamber, means for supplying fuel to said furnace chamber for combustion therein to produce high temperature heating gases, means defining a furnace outlet at the upper end of said furnace chamber, a pair of opposed upright fluidcooled walls defining a heating gas pass communicating at its inlet end with said furnace outlet, said walls being formed with recesses, and a tubular fluid heater arranged within said gas pass immediately adjacent said furnace outlet, said fluid heater including a plurality of tube platens extending between and supported by said pair of walls, each of said platens including a pair of coplanar multi-looped tubes having horizontally extending straight portions and connecting tube bends, said tubes alternately being for-med with inner and outer tube bends at opposite ends of said platen adjacent said walls, lug means disposed in said recesses attaching the uppermost outer tube 'bend at each end of said platen to said walls to thereby support the straight portions connected with said uppermost outer tube bends, and means for supporting the remaining straight portions free of direct attachment to said walls, said last named means comprising an inverted U-shaped tube engaged with one of the straight portions connected with one of the uppermost outer tube bends and extending downwardly therefrom on both sides of said platen, support bars extending between the legs of said U-shaped tube, said U-shaped tube being serially connected for flow of fluid therethrough with one of the tubes in the lower portion of said platen.

4-. A fluid heater comprising walls defining a heating chamber, means for passing high temperature heating gas through said heating chamber, and a tubular heat exchange platen within said chamber and having one end thereof adjacent one of said walls and including a multiplicity of coplanar multi-looped tubes having pairs of parallel straight portions connected at their ends by tube bends adjacent said one wall, lug means attaching the uppermost tu be bend of said platen to said one Wall to thereby support the straight portions connected with said uppermost tube bend, and means for supporting the remaining straight portions from one of the straight portions connected with said uppermost tube bend, said last named means comprising an inverted fluid-cooled U- shaped tube connected in load bearing relationship with one of the straight portions connected to said uppermost tube bend, the legs of said U-shaped tube-extending downwardly on opposite sides of said platen, and means connecting the legs of said Ushaped tube to at least some of said remaining straight portions for the support thereof.

5. A fluid heater comprising walls defining a heating chamber, means for passing high temperature heating fluid through said heating chamber, and a tubular heat exchange platen within said chamber and having one end thereof adjacent one of said walls and including a multi plicity of coplanar multi-looped tubes having pairs of parallel straight portions connected at their ends by tube 'ben-ds adjacent said one wall, lug means attaching one of said tube bends of said platen to said one wall to thereby support the straight portions connected with the attached tube bend, and means for supporting other straight portions of said platen disposed below the level of the attached tube bend from one of the straight portions connected with the attached tube bend, said last named means comprising a fluid-cooled U-shaped tube arranged in the flow circuitry of said platen and formed as an extension of one of said straight portions and connected in loadbearing relationship with one of the straight portions connected to the attached tube bend, the legs of said U- shaped tube extending downwardly from the level of the attached tube bend on opposite sides of said platen, and means connecting the legs of said U-shaped tube to at least some of said other straight portions for the support thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,920,873 1/1960 Schludenberg et a1. 122-510 3,055,348 9/1962 Brash l22-510 3,055,349 9/1962 Hamilton et al. l22-510 KENNETH W. SPRAGUE, Primary Examiner. 

5. A FLUID HEATER COMPRISING WALLS DEFINING A HEATING CHAMBER, MEANS FOR PASSING HIGH TEMPERATURE HEATING FLUID THROUGH SAID HEATING CHAMBER, AND A TUBULAR HEAT EXCHANGE PLATEN WITHIN SAID CHAMBER AND HAVING ONE END THEREOF ADJACENT ONE OF SAID WALLS AND INCLUDING A MULTIPLICITY OF COPLANAR MULTI-LOOPED TUBES HAVING PAIRS OF PARALLEL STRAIGHT PORTIONS CONNECTED AT THEIR ENDS BY TUBE BENDS ADJACENT SAID ONE WALL, LUG MEANS ATTACHING ONE OF SAID TUBE BENDS OF SAID PLATEN TO SAID ONE WALL TO THEREBY SUPPORT THE STRAIGHT PORTIONS CONNECTED WITH THE ATTACHED TUBE BEND, AND MEANS FOR SUPPORTING OTHER STRAIGHT PORTIONS OF SAID PLATEN DISPOSED BELOW THE LEVEL OF THE ATTACHED TUBE BEND FROM ONE OF THE STRAIGHT PORTIONS CONNECTED WITH THE ATTACHED TUBE BEND, SAID LAST NAMED MEANS COMPRISING A FLUID-COOLED U-SHAPED TUBE ARRANGED IN THE FLOW CIRCUITRY OF SAID PLATEN AND FORMED AS AN EXTENSION OF ONE OF SAID STRAIGHT PORTIONS AND CONNECTED IN LOADBEARING RELATIONSHIP WITH ONE OF THE STRAIGHT PORTIONS 